Plant-based diets and risk of type 2 diabetes: systematic review and dose-response meta-analysis

Type 2 diabetes (T2D) incidence has been steadily increasing over the past few decades. Several studies have evaluated the effect of plant-based, vegetarian or vegan diets on the risk of T2D, although their potential benefits need to be confirmed and characterised. We performed a literature search up to 10 July 2025, using the terms/keywords related to plant-based index (PDI), vegetarian/vegan diets and T2D. We included observational non-experimental studies evaluating adherence to such diets in adult subjects assessing T2D risk. We specifically considered overall PDI and related healthy PDI (hPDI) and unhealthy PDI (uPDI), assessing intake of different food groups. We included 36 studies published between 1999 and 2025. We found an inverse association between adherence to vegetarian/plant-based dietary patterns and T2D risk. This association was stronger, though statistically imprecise, for the vegan diet (RR = 065, 95 % CI 042, 100) and for lacto-ovo-vegetarian diet (RR = 068, 057, 082). For studies using plant-based indices, the RR were 082 (069, 082), 076 (069, 082) and 113 (098, 130) for overall PDI, hPDI and uPDI, respectively. In the dose-response meta-analysis, overall PDI and hPDI showed an inverse and almost linear association with T2D risk. Conversely, adherence to uPDI directly correlated with T2D risk. Overall, adherence to vegan/vegetarian diets may reduce T2D risk, while an unhealthy plant-based diet appears to linearly increase disease risk, indicating caution in the consumption of such unhealthy foods even if of plant origin. The beneficial association between vegetarian and healthy plant-based diets may have major public health implications.